Demountable electron tube



March 5, 1935.

1.. A; GEBHARD 1,993,724

DEMOUNTABLE ELECTRON TUBE 2 SheetsShet 1 Filed March 14, 1935 Z8 INVENTOR. v

' qp/wio a 0, ATTORNEY March 5, 1935. A. GEB HARD 1,

I I DEMOUNTABLE ELECTRON TUBE Fiied March 14, 19s: 2 Sheets-Sheet 2 IN V EN TOR.

Patented Mar. 5, 1935 UNITED STATES PATENT Q DEMOUNTABLE ELECTRON TUBE Louis A. Gebhard, Washington, I).

Application Marc hil l, 1933, Serial No. 660,707

16 cl im (01. 250 2 7.5) a I .lGranted under theact of March 3, 1883.11: amended April 30, 1928;370 G. 757) My inventionrelates broadly to electron tubes and more particularly to a construction of demountable electron tube in which the parts thereof may be readily disassembled for repair, anddefective parts replaced and the parts assembled and the tube again placed in operation.

One of the-objects of. my invention is to provide a construction of demountable electron tube having means'for readily disassembling parts of the tube to enable parts of the tube to be renewed from time to time and the tube reassembled and evacuated for continued operation.

Another object of my invention is to provide a construction. ofvhigh' power tubev having means for replacing the heaterelement of the tube when,

the heaterelement' has. deteriorated during operation of the tube.

Still another object of my invention is to provide a construction of demountable electron tube havingmeans for compensating for thermal exe pansion of the cathode under conditions of operationof the tube. i 1

A further object of my invention'is to pro vide a fluid cooled anode structure for a demountable electron tube having means for insuring an air tight assembly of the elements within the tube for evacuation from time to time for maintaining the required degree of vacuum.

Other and further objects of my invention reside in a construction of demountable electron tube. having electrodes of a construction which will readily permit assembly and disassembly of the partsof the tube for replacement of defective parts as will be set forth more fully in the-specification hereinafter following by reference to the accompanying drawings, inv which:

Figure 1 is a side elevation of an electron tube constructed in accordance with my invention; Fig. 2 is a central, vertical, longitudinal section thereof; Fig. 3 is a sectional view of a portion of the upper end of the tube showing more particularly the chuck for holding the upper end of the filament and the means employed for cooling the same; Fig. 4 is a similar View showing the 0 chuck employed for holding the lower. end of the filament and the means for cooling the same; Fig. 5 is a sectional view showing more particularly the mounting the grid; Fig. 6 is a horizontal sectional view taken on line 66 of Fig. 5; Fig. '7 is a top plan view of the tube complete; Fig. 8 .is a horizontal sectional view ,on anenlarged scale taken on line 88 of Fig. 1; Fig. 9 is a horizontal section taken on line 99 of Fig.

4; Fig. 10 is a similar View taken on line 10-40- 35 of Figq Figs. 11, 12, and 13 illustrate modified forms of gas tight'joints which may be used for insuring a gas tight closure within the tube of my invention; and Fig. 14 illustrates a" schematic form of insulated binding device which maybe used in compressing the end plates with respect 5 'to the ends of the insulated sleeves which are secured over the tubular anodej structure.

My invention is directedto a. construction of electron tube which may be assembled and dis-; assembled with ordinary tools. This is of great 10 value from an economical standpointin that the heater element, cathode or filament, may be replaced very'easily and at low cost. In tubes of the ordinary type of construction, after the filajment is burned out or the tube seriously-injured, 15 the whole tube is discarded. In the demountable tube described herein, only the damaged part or element need be-replaced. Thus the cost of operation of a radiotransmitter or other apparatus using these tubes is greatly reduced.

1 Referring to the drawings in detail, filament 1 consists of a single wire passing through the center of the tube. The use of a single wire filament permits smaller diameter of the plate and grid structures, resulting in a. more compact tube with smaller inter-element capacities. It also permits the end plates of the tubes to be the fila-' ment terminalsthus reducing the number of. insulated air tight joints in the tube to a minimum. The ends of filament 1 are held in chucks 2 and 3. Chuck 2 is secured to'a corrugated metaldisc mounted on end plate 5. Chuck 3 is mounted directly on end plate 6. A grid '7 ofcylindrical shape isalso supported from end plate 6 b'y'means of insulator 8 and insulated rod 44 which incidentally forms thegrid terminal of the tube. The insulating bushing 9 surrounds rod 44 and insulatesit' from end plate '6. The anode of cylindrical shape is shownat 10 supported 'between insulating members 11 and 12. which are also of cylindrical shape. The-tube isiheld'together by means of longitudinal insulating rods 13 extending'through the end plates 5 and 6, fastened by means of bolts 14 as shown in Fig. 2. Clearance is provided as shown at 15 between end'plate 6 and. insulating members 13 so that the joints may be properly drawn to make them air tight. g

Figs. 3 and 4 show the structure of the chucks 2 and 3 holding the filament 1." The chucks con sist of a body portion 15 having a plurality of outwardly extending jaws, slottedat 16 and formed with an appropriate recess 16b confining the end of filament 1. The ferrule 17 has an internal conical surface which engages with a correspond OFFICE ing conical surface on the chuck faces forming the extremity of the body portion and which causes tightening of the filament in the chuck when the encircling ferrule 17 is screwed home on body portion 15. To permit the turning of the ferrule its outer surface is preferably knurled or arranged to take a wrench. The means of fastening the two. chucks to the end plates differ. Fig. 3 shows the mounting on one end and Fig. 4 the mounting on the other end of the filament. The mounting shown in Fig. 3 provides a means of taking up the expansion of the filament due to the increase in temperature when heated. which is appropriately fastened to the corrugated disc 4 by welding, brazing or soldering. This makes an air tight joint. The air tight joint between 4 and 5 is made with the aid of gasket 20, ring 21 and screws 22. The tension on the filament 1 due to disc 4 is augmented by the use of a pair of flat springs 23 fastened with screws 22 and engaging with a. second integral shoulder 24 on the body portion 15, tending to urge the same upward, as clearly shown in Fig. 3.

The lower filament chuck shown in Fig. 4 is stationary. An air tight joint with an end plate 6 is accomplished through the use of a gasket 24 between the shoulder 18 on member 15 and end plate'6. The joint is tightened by a nut 25 threaded on'the body portion 15. Reference character 26 designates another gasket interposed between the nut '25 and'end plate 6. Both filament chucks are cooled by the passing of a suitable cooling fiuid through a cavity 2'7 formed inside the body portions 15. The cooling fluid enters through insulating tube 28 passing through metal tube and is ejected against the surface of the cavity 27 adjacent to the filament 1, which is the hottest surface. The liquid then passes out through metal tube 29 and insulating tube 31. The metal tubes 29 and 30 are supported from the body portion 15 by means of a plate 32 mounted at the end-of chamber 2'7. (See more particularly Fig 9.) The cavity 2'7 is tapered toward the filament 1 so as to permit greater thickness of the body portion 15 at this point. The body portion 15 thus has greater thermal conductivity andstrength and there is less liability of an air leak at this point. Better cooling of the chuck and adjacent parts is also obtained. Tube 30 is bent so that the center of its inner end coincides with the axis of 15, (see Figs. 3 and 4). r i

If the filament is burned out or injured it may be replaced by removing the chucks 2 and 3 from the tube. The chuck 2 may be removed by taking out screws 22 and lifting out the chuck. After chuck 2 has been removed chuck 3 may be taken out of the tube by loosening nut 25, pulling chuck 3 up through grid 7 and out through the hole in end plate 5. -The old filament may be taken out of the chucks by loosening the ferrulesl'l. In inserting a new filament the exact length is obtained by the use of a jig into which the chucks are placed. After the chucks havebeen tightened, the unit is placed inside the tube, the lower end passingthrough the aperture in end plate 5. The joint at the upper end plate 5 is completed first and then the lower endplate 6 is tightened by nut 25. The jig used in adjusting the length of filament is ganged so that with the filament cold it will be just a little short for the tube. Then when nut 25 is tightened, corrugated disc 19 is pulled down. Disc 19 tends to react against this pull with a spring action augmented The member 15 has a shoulder 18" by the pair of flat spring arms 23. When the filament becomes hot, it expands and this expansion is taken up by means of the disc 19 and spring arms 23. Thus the filament is always kept taut and central with respect to the tube. The body member 15 of chuck 3 has flattened sides where it passes through 6 to prevent its turning when the nut 25 is tightened, and thus torsional strains in the filament are prevented. The jig used in adjusting the filament is ganged so that the proper adjustment of the flattened portions on 15 of chuck 3 and the apertures in disc 19 through which screws 22 pass, is maintained. The filament terminals are shown at 33 and 34 connected respectively to end plates 5 and 6.

Fig. 5 shows a side elevation of the lower end of the grid structure '7 and its terminal. The grid consists of a wire spiral 35 Welded to upright rods 36 which are in turn supported by and welded to cylindrical members 37 and 38. Member 38 has laterally extending feet 39 and 40 at its lower end which serve to support the grid structure. The foot.39 is fastened to insulator 8 by means of screw 42. Insulator 8 is fastened to end plate 6 by means of stud 43. The stud 43 does not pass entirely through end plate 6 thus avoiding the troubles of another air tight joint projection.

The foot 40 is fastened to rod 44 between a washer 45 and a nut 46. Rod 44 passes through insulating bushing 9 which projects through end plate 6. A cylindrical insulating member 4'7 passes over the bushing 9 on the outer side of the end plate 6. Member 48, together with nuts'49, permits tightening to make airtight the 'joints formed with the use of gaskets and 51. The bushing 9 preferably has a shoulder 9a which engages gasket 51. The joints between anode 10 and insulating members 11 and 12 are made air tight by the use of gaskets 52 and 53, being of appropriate crosssection. Shoulders 54 and 55 are provided on anode 10 to make the joint. A filet 56 is provided at the base of the shoulder for added strength. To these shoulders is secured a cylindrical member 57 which provides a jacket around the anode 10 in which cooling fluid may circulate. Inlets 59 at opposite ends of the chamber 70, thus formed, and an outlet 61 are provided for this chamber. This arrangement provides cooling for the joints between anode 10 and insulators 11 and 12 The cooling fluid passes to portions of the anode adjacent to these joints first and thus provides maximum cooling. An anode terminal is shown at 63.

The ends of anode 10 are arranged to extend beyond the shoulders 54 and 55 and inside insulating members 12 and 11. A clearance space 62 is providedbetween the inside of these insulating members and the anode 10 This arrangement has a number of advantages. The clearance inside the tube between the anode 10 and end plates 5 and 6 can be made small thus making maximum use of the electron discharge from the filament. The grid, being mounted on end plate 6, does not interfere seriously with the extension of the anode. The surface leakage path over the insulation'is long both insideand out-.

side the tube. The clearance on the outside of the tube between anode 10 and end plates 5 and 6 'is large as it has to be in air. The clearance on the inside can be small on account of the evacuation of the tube. The insulating material is placed in a weak part of the electric field and thus the strains in it are a minimum. By the use of a cylindrical shape for insulators 11 and 12 these can easily be made and the ends ground to give a good air tight joint. The extremitiesof anode 10 are preferably rounded to increase the break-down voltage. The joints between end plates 5 and 6 and insulators 11 and 12 are made similarto those between the anode 10 and these insulators; The joints may be fluid cooled by providing members on end plates 5 and 6 adjacent to these joints and passing a cooling fluid through these chambers.

aluminum and magnesium silicates properly heat treated. The use of these materials gives low losses at radio frequencies." Afurther advantageis that the material is nonporous, preventing leakage of air into the tube. This is due to the fact that contiguous cells of the material are not connecting and are of very close texture.

This structure also permits a good joint between a ground surface and the gasket such as is used evacuated by theexhaust pump and the required vacuum automatically maintained by suitable pressure controlled mechanism. If desired, the tube may be mounted on top of the exhaust pum with suitable supports.

In addition to the advantages heretofore described in the use of the single filament there are many others. To obtain the same electron emission from a single filament as for multiple filaments, it is necessary to use a diameter with the same length which will provide equal area. This means a larger diameter filament and one which will be more rugged. Nomore power will be required to maintain it at the same temperature for the same emission. The current through the filament'will be greater and the voltage drop less. The ratio between the filament current and plate current will be greater and, therefore, the change in heating of the filament due to passage through it of the plate current willbe less. Thus the chances for localized heating are reduced to 'a minimum and a more reliable tube obtained;

The tube of my invention may be disassembled very easily for inspection of parts and replacement of those parts which are defective. One of the outstanding advantages of the design is that the filaments may be replaced without disassembling the tube, and in a very short time. The tube need not even be removed from the pump or from connection with the pump to do this. The plate and grid structures remain insimplify the illustration of the invention, these;

gaskets have been illustrated schematically in the assembly views. However, I desire that it beunderstood that in practice-the joints are formed with coacting faces establishing a serpentine course through the joint which substantially -pre- The insulating material used to make up the insulators is pref-. erably magnesium silicate or acombination of vents undesirable leakage and provides a gas tight seal.

Fig. 11 shows end plate 5 provided with an annular projection- 5a which fits into a coacting annular recess 11a in-the insulator 11. The gasket 53 which is disposed therebetween, provides a substantial seal against the leakage of gas. Fig. 12; shows a modified construction in which end plate 5 is provided with a pair of concentric ribs depending from end plate 5, as illustrated at 5?) and 50. These ribs fit into coacting annular recesses 11b and in insulator 11. The gasket 53 which is disposed between the ribs and the coacting recessesis deformed out of plane for estab-.

lishing a gas tight seal. Fig. 13 shows a further modified form ofseal in which end plate 5 has an annular projection 5d thereon having an echelon or offset annular face. The insulator 11 is provided with a coacting face which is offset in steps or echelon formation, as represented at 11d. The gasket 53, disposed between the echelon faces 5d and 11d, serves to prevent seepage. of gas between the joints. As I have pointed out, any one of the types of joint illustrated, or any other form of joint may be used for insuring a gas tight closure within the anode structure.

It will also be understood that the tension members 13 have been illustrated substantially for the purpose of simplifying the illustrations and that in practice, I employ any suitable arrangement of tension adjusting means for compressing the end plates 5 and 6 against the gasets 52, insulator 11, gaskets 53 and insulator 12,

and against the ends of the anode. One form of tension adjusting means has been illustrated in Fig. 14.1

employed for maintaining the parts of the tube in, assembled relation. I have found that these materials possess high insulating properties and can be machined. Threads 65a are out on one end of rod 65 and the rod engaged in end plate 6.

Threads 651) are cut on the opposite end of rod 65 and are engaged by nut 66, which bears against end plate 5 enabling the end plate to be compressed against the gasket, and anode assembly. 7

Various other forms of tension means may be employed, and I do not intend myinvention to be limited to the particular forms shown. 7

By reason of the fluid cooling of the chucks which support the replaceable filament andthe fluid cooling of the anode in the tube structure of my invention, a high degree of efliciency may be obtained throughout the operating life of the tube. The structure of the tube is such that the joints which must be maintained airtight are re- I tricted thereby avoiding loss of vacuum. The parts of the tube are readily replaceable and are so simplified in their construction thatthe total cost of the tube is held quite low.

While I have described the tube of my invention in one of its preferred embodiments, I desire that it be understood that modifications may be made and that no limitations upon my invention-are intended other. than are imposed by the scope of the appended claims. 7 I

-The invention herein described may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalty thereon or therefor.

What I claim as new and desire to secure by Letters Patent of the United States is as follows:

1. A demountable electron discharge device comprising a cylindrical anode forming a vacuum chamber, a plurality of elements including a filament disposed in said chamber, chuck grips mounted adjacent opposite ends of said chamber for removably supporting said filament in pos i-.

tion and permitting removal of and renewal thereof, spring means forming an integral part of said device for maintaining said filament in tension at all times, and means for directing a fluid over the inner surfaces of a portion of said fila-' one of said closure members and one of saidchuck grips for automatically maintaining tension on said filament, means for fluidcooling said chucks and said cylindrical anode, and means for evacuating the space in said chamber between said anode and said filament.

3. A demountable electron discharge device comprising a cylindrical anode forming a vacuum chamber, a plurality of elements including a filament disposed in said chamber, metallic end plates extending laterally of said chamber adjacent each end of said anode and insulated with respect thereto, said filament being formed by a single straight wire mounted centrally of said device and supported at either end by chuck grips supportedby said metallic end plates, said metallic plates constituting the filament terminals, said cylindrical anode constituting the body of the device intermediate said metallic end plates, means for fluid cooling said chucks and said anode, and means establishing connection of the device to a vacuum pump.

4. A demountable electron tube comprising a cylindrical plate electrode, an insulated sleeve engaging opposite ends of said cylindrical plate electrode, a pair of end members, tension devices interconnecting said end members, means for sealing said insulated sleeves with respect to said cylindrical plate and said end members for establishing a closed chamber within said cylindrical plate, a grid electrode extending through said chamber, a chuck device carried by each of said end members, a filament extending axially of said chamber and removably mounted at the ends thereof in said chuck device, and means for establishing a vacuum in said chamber.

5. A demountable electron tube comprising a cylindrical plate electrode, an end member insulatingly supported with each end thereof, means for drawing said end members together under tension for forming a substantially closed chamber within said cylindrical plate electrode, a grid electrode supported within said chamber, a chuck carried by each of said end members and expansible and contractible for removably receiving the opposite ends of a filament electrode.

6. A demountable electron tube comprising a cylindrical plate electrode having a central fluid cooled portion and cylindrical end portions, an insulated sleeve concentrically disposed about each end of said cylindrical plate electrode, end members disposed laterally of each of said insulated sleeves, tension members interconnecting said end members for compressing said end members against said insulated sleeves, gaskets interposed between said insulated-sleeve, said end members and said cylindrical plate electrode for establishing a substantially airtight chamber within said cylindrical plate electrode, a grid electrode mounted within said chamber, an expansible and contractible chuck carried by each of said end members, a filament electrode having its opposite ends removably gripped by each of said chucks, and means for establishing a vacuum in said chamber. 7

'7. A demountable electron tube comprising a cylindrical plate electrode, attachable cover members .insulatingly supported across each end ofsaid cylindrical plate electrode, tension. members for compressing said cover members toward the ends of said cylindrical plate electrode, means for establishing a substantially airtight chamber within said cylindrical plate electrode, a grid electrode mounted concentrically within said chamber, an expansible and contractible chuck member carried by each of said cover members, a filament wire having its opposite ends removably gripped by said chucks, and means for establishing a vacuum within said chamber.

'8. A demountable electron tube comprising a cylindrical plate electrode, a sleeve of insulation material engaging each end of said cylindrical plate electrode, a plate memberextending normal to each of said insulated sleeves, gaskets disposed between said cylindrioal plate electrode and said insulated sleeves, gaskets disposed between said insulated sleeves and said end members, tension means interconnecting said end members for compressing said end members, said gaskets and said insulated sleeves with respect to the ends of said cylindrical plate electrode for forming a substantially airtight closure, a grid electrode supported from one of said end members and extending concentrically within said cylindrical plate electrode, an expansible and'contractible chuck supported by" each of said end members, a wire-likefilament extending axially with respect to said cylindrical plate electrode and removably engaged at its opposite ends in said chucks, and means for exhausting and maintaining a vacuum within said closure.

9. A demountable electron tube comprising a cylindrical plate electrode having a double wall portion centrally thereof and a single wall exr tension on each end thereof, an insulated bushing concentrically disposed about each of said extensions, an end plate extending across each of said insulated bushings, gaskets disposed between said cylindrical plate electrode and said insulated bushings, gaskets disposed between said insulated bushings and said end plates, means for compress ingsaid end'plates against said gaskets and insulated bushings for providing a substantially airtight closure, a grid electrode insulatingly supported from one of said end members and disposed centrally within said cylindrical plate electrode, an expansible and contractible chuck supported by each of said end members, a filament having its opposite ends engageable by said chucks and extending axially of said cylindrical plate,'and means for establishing a vacuum within said closure.

10. A demountable electron tube comprising a closure member, end plates for said closure member, means for compressing said end plates against said closure member and establishing a substantially airtight connection therewith, an

expansible and contractible chuck supported from each of said end plates, 2. filament extending axially through said closure member and having the ends thereof removably engageable by said chucks, and means for evacuating saidclosure member.

11. A demountable electron tube comprising a closure member, end plates for said closure member, means for compressing said end plates against said closure member and establishing a substantially airtight connection therewith, an expansible and contractible chuck supported from each-of said end plates, a filament extending axially through said closure member and having the ends thereof removably engageable by said chucks, each of said chucks including a hollow bore extending centrally thereof for receiving a cooling fluid and being screw threaded on the exterior thereof for receiving an adjustable sleeve for clamping or releasing said chucks with respect to said filament.

12. A demountable electron tube comprising a closure member, end plates for said closure member, means for compressing said end plates against said closure member and establishing a substantially airtight connection therewith, an expansible and contractible chuck supported from each of said end plates, a filament extending axially through said closure member and having the ends thereof removably engageable by said chucks, each of said chucks having a hollow internal bore extending axially thereof, a fluid inlet port adjacent the clamping end of each of said chucks and a fluid discharge port remote from the clamping end of said chucks.

13. A demountable electron tube comprising a tubular closure member, end plates extending laterally with respect to each end of said tubular closure member, insulation means for insulatingly mounting said end plates with respect to the ends of said closure member, tension means for compressing said end plates and said insulation means with respect to the ends of said tubular closure member for providing a substantially airtight chamber within said tubular member, an expansible and contractible chuck supported by each of said end plates, a .grid electrode concentrically disposed about said chucks within said chamber, a filament havingits opposite ends removably engaged in said chucks and extending axially'of said chamber, means for fluid cooling each of said chucks, and means for establishing a vacuum within said chamber.

14. A demountable electron tube comprising a cylindrical anode, means telescopically engaging opposite ends of said anode, closure members disposed adjacent said means for providing a substantially airtight chamber within said cylindrical anode, an expansible and contractible chuck disposed centrally in one of said closure members, means for resiliently supporting an expansible and contractible chuck in the other of said closure members, a filament removably connected at each end thereof in said chucks, each of said chucks having a hollow bore extending longitudinally thereof, a fluid inlet tube projecting into the said hollow bore to a position adjacent the clamping end of said chuck, and a fluid discharge connection at the end of said bore remote from the clamping end of said chuck. I

15. A demountable electron tube comprising a tubular chamber, a .removable end closure for each end of said chamber, a corrugated diaphragm mounted centrally of one of said end closures, an expansible and contractible screw chuck mounted in said corrugated diaphragm, an expansible and contractible screw chuck carried by the other of said removable end closures, a grid electrode supported by said last mentioned end closure, and a filament having its opposite ends engaged by said screw chucks and extending axially through said tubular chamber.

16. A demountable electron tube comprising a tubular chamber, a removable end closure for each end of said chamber, an expansible and contractible screw chuck mounted in one of said removable end closures, a corrugated diaphragm disposed centrally of the other of said removable end closures, a pair of tension members disposed in spaced relation to said corrugated diaphragm, an expansible and contractible screw chuck carried by said corrugated diaphragm and engaged by said pair of tension members, and

a filament having its opposite ends removably engaged in said expansible and contractible screw chucks, said pair of tension members operating to advance or retract the screw chuck connected therewith formaintaining said'filament taut under conditions of expansion due to varying temperatures.

LOUIS A. GEBHARD. 

